Bioinformatical Analysis And Molecular Evolutionary Investigation Of NRT2Gene Family In5Woody Plants

Nitrate uptake is the first step of nitrogen utilization by plants. Nitrate transporter2（NRT2）,also called “high affinity nitrate transporter”, is one of the most importantbio-macromolecules which are involved in nitrate uptake system when nitrate concentration islow （K_m=7⁵0μM）. Bioinformatics as well as comparative and evolutionary genomicsmethods were employed to investigate the gene and protein sequences of NRT2familymembers in5woody plant species including Poplus trichocarpa, Prunus persica, Malusdomestica, Citrus sinensis and Eucalyptus grandis. The main conclusions are as follows:1. NRT2gene exists in all5woody plants while the numbers of NRT2members of eachspecies are different. There were6NRT2in P.trichocarpa,4in P.persica and M.domesticaand3in C.sinensis and E.grandis, respectively.2. NRT2gene in all5woody plants except E.grandis share similar physicochemical propertysuch as melting temperature, etc.3. All NRT2proteins were found hydrophobic with similar hydrophobic sections, despite thedifferences of each overall length.4. α-helices, followed by random coils, made up the major part of the secondary structuresformed by amino acid residues. A MFS₁domain composed by around360amino acidresidues which performed an overlap compared with the hydrophobic section was also foundin each NRT2protein. All NRT2proteins were found localized on the membrane structures incells such as cell membrane.5. All NRT2proteins in woody plants could be divided into3subfamilies. NRT2inP.trichocarpa, P.persica and M.domestica distributed in all subfamilies, while the distribution of NRT2in C.sinensis and E.grandis were incomplete （No CsiNRT2in subfamily II and noEgrNRT2in subfamily III, respectively）. Subfamily I is most conserved compared with theothers. The MFS₁domain stayed conserved during the long evolution process.6. The gene structure distribution （exons, introns, etc.） of NRT2in each subfamily were foundextremely similar. Intron deletion or other events might occured during the evolution processduring which lower plants developed into higher plants.7. The codon adaptive index （CAI） of coding sequences in PtrNRT2, PpeNRT2, MdoNRT2and CsiNRT2were found less than it in EgrNRT2, while the effective number of codons（ENC） showed a contrary. There is a higher translation initiation of CDS in EgrNRT2genes.8. Purifying selection pressure other than site mutation was found the major factor influencingthe evolution of NRT2gene coding sequences except some certain amino acid sites.